Using sulphur isotopes

Equations governing the fractionation of 0 (temperature in keivin units unless otherwise stated) 

There are four stable isotopes of sulphur which have the following abundances  

Island-arc basalts + andesites Volcanic H2S Volcanic SOj Granites 

The ratio between the two most abundant isotopes, S/ S, is used in geochemistry and expressed in parts per thousand relative to the reference standard of troilite (FeS) from the Canon Diablo iron meteorite (CDT) in the form 34s/32s (sample) — (standard)  

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Using sulphur isotopes to understand the genesis of hydrothermai ore deposits... 

Giesemann A, Jager HA, Norman AL, Krouse HR, Brand WA (1994) On-line sulphur isotope determination using an elemental analyzer coupled to a mass spectrometer. Anal Chem 66 2816-2819... 

Redding CE, SchoeU M, Monin JC, Durand B (1980) Hydrogen and carbon isotopic composition of coals and kerogen. In Douglas AG, Maxwell JR (eds.) Phys Chem Earth 12 711-723 Rees CE (1978) Sulphur isotope measurements using S02and SFg. Geochim Cosmochim Acta 42 383-389... 

Recent work by Wilson Orr ( ) and others using stable isotope techniques has provided strong evidence that incorporation from an inorganic source is the most probable explanation. Inorganic sulphur (sulphate) tends to be richer in the heavy sulphur isotope, compared with reference meteoritic sulphur... 

Phosphorus-32, for example, produced by irradiating sulphur or natural phosphorus ( P) with high-energy particles, has a half-life of 14.8 days and can be rapidly taken up (in the form of phosphate) by body tissues such as muscles, the liver, bones, and teeth. De Hevesy found that different phosphorus compounds would be incorporated in a tissue-specific manner certain compounds were concentrated in the liver, for example. One can use stable isotopes as biological tracers too, since they are detectable atom by atom using mass spectrometry. De Hevesy observed that it takes deuterium twenty-six minutes to pass from ingested heavy water into urine. 

Whereas conventional methods for analysing sulphur isotope compositions need >10 mg of physically separated sample and long analytical times, in contrast, the EA-IRMS technique uses small samples (1-2 mg) and has short analysis times. This achieves the high physical resolution and large sample populations needed for adequate study of biological variation in Archaean sulphide-rich organic sediments. 

We would like to thank the following friends and colleagues who have helped us with various aspects of the preparation of this book Tim Atkinson, Rachel Cave, Tony Greenaway, Robin Haynes, Kevin Hiscock, Alan Kendall, Gill Malin, John McArthur, Rachel Mills, Willard Pinnock, Annika Swindell and Elvin Thurston. Special thanks are due to Nicola McArdle for permission to use some of her sulphur isotope data. 

Another major increase in atmospheric 02 may have occurred towards the end of the Proterozoic (Knoll et al. 1986 Derry et al. 1992 Des Marais et al. 1992), providing the opportunity for more complex, multicellular eukaryotes to evolve. Further evidence for such an increase is provided by the isotopic record of sedimentary marine sulphides (Canfield 1998 see Box 1.13). From c.2.3 to between 1.05 and 0.64 Ga the sulphur isotopic fractionation was <4%o with respect to marine sulphate, suggesting low sulphate levels, consistent with limited oxygenation of the atmosphere and surface waters, sufficient to allow enough oxidation of sulphide to sulphate for the use of sulphate-reducing bacteria in deeper anoxic environments. Enough sulphide may have been produced by these bacteria to remove dissolved iron(II) as pyrite. So for a large part of the Proterozoic bottom waters remained anoxic and sulphidic... 

MacAvoy S.E., Macko S.A., Garman G.C. (1998) Tracing marine biomass into tidal freshwater ecosystems using stable sulphur isotopes. Naturwissenschaften 85, 544—6. 

Eiler JM, Kitchen N, Rahn TA (2000) Experimental constraints on the stable-isotope systematics of CO2 ice/vapor systems and relevance to the study of Mars. Geochim Cosmochim Acta 64 733-746 Elcombe MM, Hulston JR (1975) Calculation of sulphur isotope fractionation between sphalerite and galena using lattice dynamics. Earth Planet Sci Lett 28 172-180 Emiliani C (1955) Pleistocene paleotemperatures. J Geol 63 538-578... 

Tigure 7.24 Parddoning of between mineral pairs and H2S-SO2 as a funedon of temperature. These fracdonadon curves can be used -in sulphur isotope thermometry and indicate that the. greatest fracdonadons are between sulphides, and sulphate minerals. 

Figure 7,26 Parddoning of between minerals and H S as a function of temperature. These fracdonadon curves are used as a basis for the sulphur isotope thermometers given in Box 7.5. Mineral-pairs showing the greatest separation on diis diagram will be the most sensitive thermometers (mainly after Ohmoto and Rye, 1979).

Isotopic composition of sulphur S is determined usually by the ratio (4 stable isotopes - S, and - are known). This ratio is most stable in meteorites. That is why as standard is used the sulphur isotopic composition in troilite (FeS) from the meteorite in the Canyon Diablo Troilite (CDT) where the ratio is 1/22.22. 

Bourns (1963) investigated the bromination of anisole-4-sulphonic-2,6- 2 acid. In the presence of 0 0 to 2-Om bromide ions the ratio kgjkjy increases from 1-00 to 1-31. As a competitive reaction bromode-sulphonation takes place, bromine substituting the sulphonic group in the 4-position. Using anisole-4-sulphonic acid containing the natural abundance of the sulphur isotopes. Bourns measured sulphur isotope effects k jk is 1-003, 1-013 and 1-017 for initial bromide ion concentrations of 0-0, 0-05 and 0-50m respectively. This confirms, that bromodesulphonation also follows mechanism (6-2). 

Although little work has been reported on the use of sulphur isotopes in areas of interest to the medicinal chemist, sulphur-34 could well play a significant role in the future. Some comments, therefore, are not out of place. 

There could be other methods such as the use of sulphur isotopes that have a lighter atomic number so that when they react with micro-organism-driven sulphate reduction (for exanple SRB), they can easily be identified fiom the non-biologically formed heavier sulphur isotope compounds. 

A more detailed study of the nitration of quinolinium (l) in 80-05 % sulphuric acid at 25 °C, using isotopic dilution analysis, has shown that 3-) 5-) 6-, 7- and 8-nitroquinoline are formed (table 10.3). Combining these results with the kinetic ones, and assuming that no 2- and 4-nitration occurs, gives the partial rate factors listed in table 10.4. Isoquinolinium is 14 times more reactive than quinolinium. The strong deactivation of the 3-position is in accord with an estimated partial rate factor of io for hydrogen isotope exchange at the 3-position in the pyridinium ion. It has been estimated that the reactivity of this ion is at least 10 less than that of the quinolinium ion. Based on this estimate, the partial rate factor for 3-nitration of the pyridinium ion would be less than 5 x io . 

The isotopic composition of carbon in carbonaceous organic material (kerogen) from ancient sedimentary rocks gives information on whether photosynthetic organisms were present during rock formation or not. It can also provide information on biological activities if cellular structures had already been destroyed. Sulphur can be used in a similar way (Schopf, 1999). 

These are unstable forms of elements which decay by the emission of radiation. A radioactive isotope of an element behaves chemically in the same way as the non-radioactive form, but its radiation may be detected and measured by a suitable instrument. In the rubber industry radioactive isotopes are used in beta ray thickness gauges, in studying the precise role of sulphur in vulcanisation, in the speedy determination of tread wear in tyres, etc. See Beta Rays. 

Crystallisation was one of the earliest methods used for separation of radioactive microcomponents from a mass of inert material. Uranium X, a thorium isotope, is readily concentrated in good yield in the mother liquors of crystallisation of uranyl nitrate (11), (33), (108). A similar method has been used to separate sulphur-35 [produced by the (n, p) reaction on chlorine-35] from pile irradiated sodium ot potassium chloride (54), (133). Advantage is taken of the low solubility of the target materials in concentrated ice-cold hydrochloric acid, when the sulphur-35 as sulphate remains in the mother-liquors. Subsequent purification of the sulphur-35 from small amounts of phosphorus-32 produced by the (n, a) reaction on the chlorine is, of course, required. Other examples are the precipitation of barium chloride containing barium-1 from concentrated hydrochloric acid solution, leaving the daughter product, carrier-free caesium-131, in solution (21) and a similar separation of calcium-45 from added barium carrier has been used (60). 

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